Surgical navigation systems and processes for unicompartmental knee arthroplasty

ABSTRACT

Systems and processes for tracking anatomy, instrumentation, trial implants, implants, and references, and rendering images and data related to them in connection with surgical operations, for example unicompartmental knee arthroplasties (“UKA”). These systems and processes are accomplished by using a computer to intraoperatively obtain images of body parts and to register, navigate, and track surgical instruments.

RELATED APPLICATION DATA

[0001] This document claims the benefit of U.S. Ser. No. 60/271,818,filed Feb. 27, 2001 entitled “Image Guided System for Arthroplasty” andU.S. Ser. No. 60/355,899, filed Feb. 11, 2002 entitled “SurgicalNavigation Systems and Processes,” which documents are incorporatedherein by this reference.

FIELD OF THE INVENTION

[0002] This invention generally relates to unicompartmental kneearthroplasty surgical operations using systems and processes fortracking anatomy, implements, instrumentation, trial implants, implantcomponents and virtual constructs or references, and rendering imagesand data related to them. Anatomical structures and such items may beattached to or otherwise associated with fiducial functionality, andconstructs may be registered in position using fiducial functionalitywhose position and orientation can be sensed and tracked by systems andaccording to processes of the present invention in three dimensions inorder to perform unicompartmental knee arthroplasty. Such structures,items and constructs can be rendered onscreen properly positioned andoriented relative to each other using associated image files, datafiles, image input, other sensory input, based on the tracking. Suchsystems and processes, among other things, allow surgeons to navigateand perform unicompartmental knee arthroplasty using images that revealinterior portions of the body combined with computer generated ortransmitted images that show surgical implements, instruments, trials,implants, and/or other devices located and oriented properly relative tothe body part. Such systems and processes allow, among other things,more accurate and effective resection of bone, placement and assessmentof trial implants and joint performance, and placement and assessment ofperformance of actual implants and joint performance.

BACKGROUND

[0003] Knee arthroplasty is a surgical procedure in which the articularsurfaces of the femur, tibia and patella are cut away and replaced bymetal and/or plastic prosthetic components. The goals of kneearthroplasty include resurfacing the bones in the knee joint andrepositioning the joint center on the mechanical axis of the leg. Kneearthroplasty is generally recommended for patients with severe knee painand disability caused by damage to cartilage from rheumatoid arthritis,osteoarthritis or trauma. It can be highly successful in relieving painand restoring joint function.

[0004] More than 95% of knee arthroplasties performed in the UnitedStates are tricompartmental knee arthroplasties (“TKA”), which involvesthe replacement of all the articular surfaces of the knee joint. TKA isperformed when arthritis or trauma has affected two or more of the threecompartments of the knee: medial compartment (toward the body's centralaxis), lateral compartment (away from the body's central axis), andpatello-femoral compartment (toward the front of the knee).

[0005] The remaining knee arthroplasties are unicompartmental kneearthroplasties (“UKA”). UKA involves the replacement of the articularsurfaces of only one knee compartment, usually the medial compartment.UKA is an attractive surgical treatment for patients with arthritis inonly one compartment and with a healthy patella.

[0006] UKA has several advantages over TKA. UKA allows the preservationof both cruciate ligaments, while the anterior cruciate ligament isusually removed in TKA. Preservation of the ligaments provides greaterstability to the joint after surgery. UKA also allows for preservationof more bone stock at the joint, which will be beneficial if revisioncomponents must be placed. Finally, UKA is less invasive than TKAbecause UKA requires smaller resections and components.

[0007] In spite of these advantages, there continue to be problems inUKA performance. A leading cause of wear and revision in prostheticssuch as knee implants, hip implants and shoulder implants is less thanoptimum implant alignment. In a UKA, for example, current instrumentdesign for resection of bone limits the alignment of the femoral andtibial resections to average values for varus/valgus flexion/extension,and external/internal rotation. Additionally, surgeons often use visuallandmarks or “rules of thumb” for alignment which can be misleading dueto anatomical variability. Intramedullary referencing instruments alsoviolate the femoral and tibial canal. This intrusion increases the riskof fat embolism and unnecessary blood loss in the patient. Surgeons alsorely on instrumentation to predict the appropriate implant size for thefemur and tibia instead of the ability to intraoperatively template theappropriate size of the implants for optimal performance. Anotherchallenge for surgeons is soft tissue or ligament balancing after thebone resections have been made. Releasing some of the soft tissue pointscan change the balance of the knee; however, the multiple options can beconfusing for many surgeons. Although much of the bone stock remainsafter UKA, if a revision is necessary, many of the visual landmarks areno longer present, making alignment and restoration of the joint linedifficult.

SUMMARY

[0008] The present invention is applicable not only for knee repair,reconstruction or replacement surgery, but also repair, reconstructionor replacement surgery in connection with any other joint of the body aswell as any other surgical or other operation where it is useful totrack position and orientation of body parts, non-body components and/orvirtual references such as rotational axes, and to display and outputdata regarding positioning and orientation of them relative to eachother for use in navigation and performance of the operation.

[0009] Systems and processes according to one embodiment of the presentinvention use position and/or orientation tracking sensors such asinfrared sensors acting stereoscopically or otherwise to track positionsof body parts, surgery-related items such as implements,instrumentation, trial prosthetics, prosthetic components, and virtualconstructs or references such as rotational axes which have beencalculated and stored based on designation of bone landmarks. Processingcapability such as any desired form of computer functionality, whetherstandalone, networked, or otherwise, takes into account the position andorientation information as to various items in the position sensingfield (which may correspond generally or specifically to all or portionsor more than all of the surgical field) based on sensed position andorientation of their associated fiducials or based on stored positionand/or orientation information. The processing functionality correlatesthis position and orientation information for each object with storedinformation regarding the items, such as a computerized fluoroscopicimaged file of a femur or tibia, a wire frame data file for rendering arepresentation of an instrumentation component, trial prosthesis oractual prosthesis, or a computer generated file relating to a rotationalaxis or other virtual construct or reference. The processingfunctionality then displays position and orientation of these objects ona screen or monitor, or otherwise. Thus, systems and processes accordingto one embodiment of the invention can display and otherwise outputuseful data relating to predicted or actual position and orientation ofbody parts, surgically related items, implants, and virtual constructsfor use in navigation, assessment, and otherwise performing surgery orother operations.

[0010] As one example, images such as fluoroscopy images showinginternal aspects of the femur and tibia can be displayed on the monitorin combination with actual or predicted shape, position and orientationof surgical implements, instrumentation components, trial implants,actual prosthetic components, and rotational axes in order to allow thesurgeon to properly position and assess performance of various aspectsof the knee joint being repaired, reconstructed or replaced. The surgeonmay navigate tools, instrumentation, trial prostheses, actual prosthesesand other items relative to the femur and tibia in order to performUKA's more accurately, efficiently, and with better alignment andstability.

[0011] Systems and processes according to the present invention can alsouse the position tracking information and, if desired, data relating toshape and configuration of surgical related items and virtual constructsor references in order to produce numerical data which may be used withor without graphic imaging to perform tasks such as assessingperformance of trial prosthetics statically and throughout a range ofmotion, appropriately modifying tissue such as ligaments to improve suchperformance and similarly assessing performance of actual prostheticcomponents which have been placed in the patient for alignment andstability.

[0012] Systems and processes according to the present invention can alsogenerate data based on position tracking and, if desired, otherinformation to provide cues on screen, aurally or as otherwise desiredto assist in the surgery such as suggesting certain bone modificationsteps or measures which may be taken to release certain ligaments orportions of them based on performance of components as sensed by systemsand processes according to the present invention.

[0013] According to a preferred embodiment of systems and processesaccording to the present invention, at least the following steps areinvolved:

[0014] 1. Obtain appropriate images such as fluoroscopy images ofappropriate body parts such as femur and tibia, the imager being trackedin position via an associated fiducial whose position and orientation istracked by position/orientation sensors such as stereoscopic infrared(active or passive) sensors according to the present invention.

[0015] 2. Register tools, instrumentation, trial components, prostheticcomponents, and other items to be used in surgery, each of whichcorresponds to a fiducial whose position and orientation can be trackedby the position/orientation sensors.

[0016] 3. Locating and registering body structure such as designatingpoints on the femur and tibia using a probe associated with a fiducialin order to provide the processing functionality information relating tothe body part such as rotational axes.

[0017] 4. Navigating and positioning instrumentation such as cuttinginstrumentation in order to modify bone, at least partially using imagesgenerated by the processing functionality corresponding to what is beingtracked and/or has been tracked, and/or is predicted by the system, andthereby resecting bone effectively, efficiently and accurately.

[0018] 5. Navigating and positioning trial components such as femoralcomponents and tibial components, some or all of which may be installedusing impactors with a fiducial and, if desired, at the appropriate timediscontinuing tracking the position and orientation of the trialcomponent using the impactor fiducial and starting to track thatposition and orientation using the body part fiducial on which thecomponent is installed.

[0019] 6. Assessing alignment and stability of the trial components andjoint, both statically and dynamically as desired, using images of thebody parts in combination with images of the trial components whileconducting appropriate rotation, anterior-posterior drawer andflexion/extension tests and automatically storing and calculatingresults to present data or information which allows the surgeon toassess alignment and stability.

[0020] 7. Releasing tissue such as ligaments if necessary and adjustingtrial components as desired for acceptable alignment and stability.

[0021] 8. Installing implant components whose positions may be trackedat first via fiducials associated with impactors for the components andthen tracked via fiducials on the body parts in which the components areinstalled.

[0022] 9. Assessing alignment and stability of the implant componentsand joint by use of some or all tests mentioned above and/or other testsas desired, releasing tissue if desired, adjusting if desired, andotherwise verifying acceptable alignment, stability and performance ofthe prosthesis, both statically and dynamically.

[0023] This process, or processes including it or some of it may be usedin any total or partial joint repair, reconstruction or replacement,including knees, hips, shoulders, elbows, ankles and any other desiredjoint in the body.

[0024] Systems and processes according to the present inventionrepresent significant improvement over other previous systems andprocesses. For instance, systems which use CT and MRI data generallyrequire the placement of reference frames pre-operatively which can leadto infection at the pin site. The resulting 3D images must then beregistered, or calibrated, to the patient anatomy intraoperatively.Current registration methods are less accurate than the fluoroscopicsystem. These imaging modalities are also more expensive. Some“imageless” systems, or non-imaging systems, require digitizing a largenumber of points to define the complex anatomical geometries of the kneeat each desired site. This can be very time intensive resulting inlonger operating room time. Other imageless systems determine themechanical axis of the knee by performing an intraoperative kinematicmotion to determine the center of rotation at the hip, knee, and ankle.This requires placement of reference frames at the iliac crest of thepelvis and in or on the ankle. This calculation is also time consumingat the system must find multiple points in different planes in order tofind the center of rotation. This is also problematic in patients withpathologic conditions. Ligaments and soft tissues in the arthriticpatient are not normal and thus will give a center of rotation that isnot desirable for normal knees. Robotic systems require expensive CT orMRI scans and also require pre-operative placement of reference frames,usually the day before surgery. These systems are also much slower,almost doubling operating room time and expense.

[0025] None of these systems can effectively track femoral and/or tibialtrials during a range of motion and calculate the relative positions ofthe articular surfaces, among other things. Also, none of them currentlymake suggestions on ligament balancing, display ligament balancingtechniques, or surgical techniques. Additionally, none of these systemscurrently track the patella.

[0026] An object of certain aspects of the present invention is to usecomputer processing functionality in combination with imaging andposition and/or orientation tracking sensors to present to the surgeonduring surgical operations visual and data information useful tonavigate, track and/or position implements, instrumentation, trialcomponents, prosthetic components and other items and virtual constructsrelative to the human body in order to improve performance of arepaired, replaced or reconstructed knee joint.

[0027] Another object of certain aspects of the present invention is touse computer processing functionality in combination with imaging andposition and/or orientation tracking sensors to present to the surgeonduring surgical operations visual and data information useful to assessperformance of a knee and certain items positioned therein, includingcomponents such as trial components and prosthetic components, forstability, alignment and other factors, and to adjust tissue and bodyand non-body structure in order to improve such performance of arepaired, reconstructed or replaced knee joint.

[0028] Another object of certain aspects of the present invention is touse computer processing functionality in combination with imaging andposition and/or orientation tracking sensors to present to the surgeonduring surgical operations visual and data information useful to showany or all of predicted position and movement of implements,instrumentation, trial components, prosthetic components and other itemsand virtual constructs relative to the human body in order to selectappropriate components, resect bone accurately, effectively andefficiently, and thereby improve performance of a repaired, replaced orreconstructed knee joint.

[0029] Other objects, features and advantages of the present inventionare apparent with respect to the remainder of this document.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a schematic view of a particular embodiment of systemsand processes according to the present invention.

[0031]FIG. 2 is a view of a knee prepared for surgery, including a femurand a tibia to which fiducials according to one embodiment of thepresent invention have been attached.

[0032]FIG. 3 is a view of a portion of a leg prepared for surgeryaccording to the present invention with a C-arm for obtainingfluoroscopic images associated with a fiducial according to oneembodiment of the present invention.

[0033]FIG. 4 is a fluoroscopic image of free space rendered on a monitoraccording to one embodiment of the present invention.

[0034]FIG. 5 is a fluoroscopic image of femoral head obtained andrendered according one embodiment of the present invention.

[0035]FIG. 6 is a fluoroscopic image of a knee obtained and renderedaccording to one embodiment of the present invention.

[0036]FIG. 7 is a fluoroscopic image of a tibia distal end obtained andrendered according to one embodiment of the present invention.

[0037]FIG. 8 is a fluoroscopic image of a lateral view of a kneeobtained and rendered according to one embodiment of the presentinvention,

[0038]FIG. 9 is a fluoroscopic image of a lateral view of a kneeobtained and rendered according to one embodiment of the presentinvention.

[0039]FIG. 10 is a fluoroscopic image of a lateral view of a tibiadistal end obtained and rendered according to one embodiment of thepresent invention.

[0040]FIG. 11 shows a probe according to one embodiment of the presentinvention being used to register a surgically related component fortracking according to one embodiment of the present invention.

[0041]FIG. 12 shows a probe according to one embodiment of the presentinvention being used to register a cutting block for tracking accordingto one embodiment of the present invention.

[0042]FIG. 13 shows a probe according to one embodiment of the presentinvention being used to register a tibial cutting block for trackingaccording to one embodiment of the present invention.

[0043]FIG. 14 shows a probe according to one embodiment of the presentinvention being used to register an alignment guide for trackingaccording to one embodiment of the present invention.

[0044]FIG. 15 shows a probe according to one embodiment of the presentinvention being used to designate landmarks on bone structure fortracking according one embodiment of the present invention.

[0045]FIG. 16 is another view of a probe according to one embodiment ofthe present invention being used to designate landmarks on bonestructure for tracking according one embodiment of the presentinvention.

[0046]FIG. 17 is another view of a probe according to one embodiment ofthe present invention being used to designate landmarks on bonestructure for tracking according one embodiment of the presentinvention.

[0047]FIG. 18 is a screen face produced according to one embodiment ofthe present invention during designation of landmarks to determine afemoral mechanical axis.

[0048]FIG. 19 is a view produced according to one embodiment of thepresent invention during designation of landmarks to determine a tibialmechanical axis.

[0049]FIG. 20 is a screen face produced according to one embodiment ofthe present invention during designation of landmarks to determine anepicondylar axis.

[0050]FIG. 21 is a screen face produced according to one embodiment ofthe present invention during designation of landmarks to determine ananterior-posterior axis.

[0051]FIG. 22 is a screen face produced according to one embodiment ofthe present invention during designation of landmarks to determine aposterior condylar axis.

[0052]FIG. 23 is a screen face according to one embodiment of thepresent invention which presents graphic indicia which may be employedto help determine reference locations within bone structure.

[0053]FIG. 24 is a screen face according to one embodiment of thepresent invention showing mechanical and other axes which have beenestablished according to one embodiment of the present invention.

[0054]FIG. 25 is another screen face according to one embodiment of thepresent invention showing mechanical and other axes which have beenestablished according to one embodiment of the present invention.

[0055]FIG. 26 is another screen face according to one embodiment of thepresent invention showing mechanical and other axes which have beenestablished according to one embodiment of the present invention.

[0056]FIG. 27 shows navigation and placement of an extramedullary rodaccording to one embodiment of the present invention.

[0057]FIG. 28 is another view showing navigation and placement of anextramedullary rod according to one embodiment of the present invention.

[0058]FIG. 29 is a screen face produced according to one embodiment ofthe present invention which assists in navigation and/or placement of anextramedullary rod.

[0059]FIG. 30 is another view of a screen face produced according to oneembodiment of the present invention which assists in navigation and/orplacement of an extramedullary rod.

[0060]FIG. 31 is a view which shows navigation and placement of analignment guide according to one embodiment of the present invention.

[0061]FIG. 32 is another view which shows navigation and placement of analignment guide according to one embodiment of the present invention.

[0062]FIG. 33 is a view showing placement of an alignment guideaccording to one embodiment of the present invention.

[0063]FIG. 34 is another view showing placement of a cutting blockaccording to one embodiment of the present invention.

[0064]FIG. 35 is a view showing navigation and placement of the cuttingblock of FIG. 45.

[0065]FIG. 36 is another view showing navigation and placement of acutting block according to one embodiment of the present invention.

[0066]FIG. 37 is a view showing navigation and placement of a tibialcutting block according to one embodiment of the present invention.

[0067]FIG. 38 is a view showing the UKA femoral and tibial implantcomponents.

[0068]FIG. 39 is a view showing the UKA femoral and tibial implantcomponents attached at the knee joint.

DETAILED DESCRIPTION

[0069] Systems and processes according to a preferred embodiment of thepresent invention use computer capacity, including standalone and/ornetworked, to store data regarding spatial aspects of surgically relateditems and virtual constructs or references including body parts,implements, instrumentation, trial components, prosthetic components androtational axes of body parts. Any or all of these may be physically orvirtually connected to or incorporate any desired form of mark,structure, component, or other fiducial or reference device or techniquewhich allows position and/or orientation of the item to which it isattached to be sensed and tracked, preferably in three dimensions oftranslation and three degrees of rotation as well as in time if desired.

[0070] In a preferred embodiment, orientation of the elements on aparticular fiducial varies from one fiducial to the next so that sensorsaccording to the present invention may distinguish between variouscomponents to which the fiducials are attached in order to correlate fordisplay and other purposes data files or images of the components. In apreferred embodiment of the present invention, some fiducials usereflective elements and some use active elements, both of which may betracked by preferably two, sometimes more infrared sensors whose outputmay be processed in concert to geometrically calculate position andorientation of the item to which the fiducial is attached.

[0071] Position/orientation tracking sensors and fiducials need not beconfined to the infrared spectrum. Any electromagnetic, electrostatic,light, sound, radiofrequency or other desired technique may be used.Alternatively, each item such as a surgical implement, instrumentationcomponent, trial component, implant component or other device maycontain its own “active” fiducial such as a microchip with appropriatefield sensing or position/orientation sensing functionality andcommunications link such as spread spectrum RF link, in order to reportposition and orientation of the item. Such active fiducials, or hybridactive/passive fiducials such as transponders can be implanted in thebody parts or in any of the surgically related devices mentioned above,or conveniently located at their surface or otherwise as desired.Fiducials may also take the form of conventional structures such as ascrew driven into a bone, or any other three dimensional item attachedto another item, position and orientation of such three dimensional itemable to be tracked in order to track position and orientation of bodyparts and surgically related items. Hybrid fiducials may be partlypassive, partly active such as inductive components or transponderswhich respond with a certain signal or data set when queried by sensorsaccording to the present invention.

[0072] Systems and processes according to a preferred embodiment of thepresent invention employ a computer to calculate and store referenceaxes of body components such as in a UKA, for example, the mechanicalaxis of the femur and tibia. From these axes such systems track theposition of the instrumentation and osteotomy guides so that boneresections will locate the implant position optimally, usually alignedwith the mechanical axis. Furthermore, during trial reduction of theknee, the systems provide feedback on the balancing of the ligaments ina range of motion and under varus/valgus, anterior/posterior and rotarystresses and can suggest or at least provide more accurate informationthan in the past about which ligaments the surgeon should release inorder to obtain correct balancing, alignment and stability. Systems andprocesses according to the present invention can also suggestmodifications to implant size, positioning, and other techniques toachieve optimal kinematics. Systems and processes according to thepresent invention can also include databases of information regardingtasks such as ligament balancing, in order to provide suggestions to thesurgeon based on performance of test results as automatically calculatedby such systems and processes.

[0073]FIG. 1 is a schematic view showing one embodiment of a systemaccording to the present invention and one version of a settingaccording to the present invention in which surgery on a knee, in thiscase a Unicompartmental Knee Arthroplasty, may be performed. Systems andprocesses according to the present invention can track various bodyparts such as tibia 10 and femur 12 to which fiducials of the sortdescribed above or any other sort may be implanted, attached, orotherwise associated physically, virtually, or otherwise. In theembodiment shown in FIG. 1, fiducials 14 are structural frames some ofwhich contain reflective elements, some of which contain LED activeelements, some of which can contain both, for tracking usingstereoscopic infrared sensors suitable, at least operating in concert,for sensing, storing, processing and/or outputting data relating to(“tracking”) position and orientation of fiducials 14 and thuscomponents such as 10 and 12 to which they are attached or otherwiseassociated. Position sensor 16, as mentioned above, may be any sort ofsensor functionality for sensing position and orientation of fiducials14 and therefore items with which they are associated, according towhatever desired electrical, magnetic, electromagnetic, sound, physical,radio frequency, or other active or passive technique. In the preferredembodiment, position sensor 16 is a pair of infrared sensors disposed onthe order of a meter, sometimes more, sometimes less, apart and whoseoutput can be processed in concert to provide position and orientationinformation regarding fiducials 14.

[0074] In the embodiment shown in FIG. 1, computing functionality 18 caninclude processing functionality, memory functionality, input/outputfunctionality whether on a standalone or distributed basis, via anydesired standard, architecture, interface and/or network topology. Inthis embodiment, computing functionality 18 is connected to a monitor onwhich graphics and data may be presented to the surgeon during surgery.The screen preferably has a tactile interface so that the surgeon maypoint and click on screen for tactile screen input in addition to orinstead of, if desired, keyboard and mouse conventional interfaces.Additionally, a foot pedal 20 or other convenient interface may becoupled to functionality 18 as can any other wireless or wirelineinterface to allow the surgeon, nurse or other desired user to controlor direct functionality 18 in order to, among other things, captureposition/orientation information when certain components are oriented oraligned properly. Items 22 such as trial components, instrumentationcomponents may be tracked in position and orientation relative to bodyparts 10 and 12 using fiducials 14.

[0075] Computing functionality 18 can process, store and output onmonitor 24 and otherwise various forms of data which correspond in wholeor part to body parts 10 and 12 and other components for item 22. Forexample, in the embodiment shown in FIG. 1, body parts 10 and 12 areshown in cross-section or at least various internal aspects of them suchas bone canals and surface structure are shown using fluoroscopicimages. These images are obtained using a C-arm attached to a fiducial14. The body parts, for example, tibia 10 and femur 12, also havefiducials attached. When the fluoroscopy images are obtained using theC-arm with fiducial 14, a position/orientation sensor 16 “sees” andtracks the position of the fluoroscopy head as well as the positions andorientations of the tibia 10 and femur 12. The computer stores thefluoroscopic images with this position/orientation information, thuscorrelating position and orientation of the fluoroscopic image relativeto the relevant body part or parts. Thus, when the tibia 10 andcorresponding fiducial 14 move, the computer automatically andcorrespondingly senses the new position of tibia 10 in space and cancorrespondingly move implements, instruments, references, trials and/orimplants on the monitor 24 relative to the image of tibia 10. Similarly,the image of the body part can be moved, both the body part and suchitems may be moved, or the on screen image otherwise presented to suitthe preferences of the surgeon or others and carry out the imaging thatis desired. Similarly, when an item 22, such as an extramedullary rod,intramedullar rod, or any other type of rod, that is being trackedmoves, its image moves on monitor 24 so that the monitor shows the item22 in proper position and orientation on monitor 24 relative to thefemur 12: The rod 22 can thus appear on the monitor 24 in proper orimproper alignment with respect to the mechanical axis and otherfeatures of the femur 12, as if the surgeon were able to see into thebody in order to navigate and position rod 22 properly.

[0076] The computer functionality 18 can also store data relating toconfiguration, size and other properties of items 22 such as implements,instrumentation, trial components, implant components and other itemsused in surgery. When those are introduced into the field ofposition/orientation sensor 16, computer functionality 18 can generateand display overlain or in combination with the fluoroscopic images ofthe body parts 10 and 12, computer generated images of implements,instrumentation components, trial components, implant components andother items 22 for navigation, positioning, assessment and other uses.

[0077] Additionally, computer functionality 18 can track any point inthe position/orientation sensor 16 field such as by using a designatoror a probe 26. The probe also can contain or be attached to a fiducial14. The surgeon, nurse, or other user touches the tip of probe 26 to apoint such as a landmark on bone structure and actuates the foot pedal20 or otherwise instructs the computer 18 to note the landmark position.The position/orientation sensor 16 “sees” the position and orientationof fiducial 14 “knows” where the tip of probe 26 is relative to thatfiducial 14 and thus calculates and stores, and can display on monitor24 whenever desired and in whatever form or fashion or color, the pointor other position designated by probe 26 when the foot pedal 20 is hitor other command is given. Thus, probe 26 can be used to designatelandmarks on bone structure in order to allow the computer 18 to storeand track, relative to movement of the bone fiducial 14, virtual orlogical information such as mechanical axis 28, medial laterial axis 30and anterior/posterior axis 32 of femur 12, tibia 10 and other bodyparts in addition to any other virtual or actual construct or reference.

[0078] Systems and processes according to an embodiment of the presentinvention such as the subject of FIGS. 2-36, can use the so-calledFluoroNAV system and software provided by Medtronic Sofamor DanekTechnologies. Such systems or aspects of them are disclosed in U.S. Pat.Nos. 5,383,454; 5,871,445; 6,146,390; 6,165,81; 6,235,038 and 6,236,875,and related (under 35 U.S.C. Section 119 and/or 120) patents, which areall incorporated herein by this reference. Any other desired systems canbe used as mentioned above for imaging, storage of data, tracking ofbody parts and items and for other purposes.

[0079] The FluoroNav system requires the use of reference frame typefiducials 14 which have four and in some cases five elements tracked byinfrared sensors for position/orientation of the fiducials and thus ofthe body part, implement, instrumentation, trial component, implantcomponent, or other device or structure being tracked. Such systems alsouse at least one probe 26 which the surgeon can use to select,designate, register, or otherwise make known to the system a point orpoints on the anatomy or other locations by placing the probe asappropriate and signaling or commanding the computer to note thelocation of, for instance, the tip of the probe. The FluoroNav systemalso tracks position and orientation of a C-arm used to obtainfluoroscopic images of body parts to which fiducials have been attachedfor capturing and storage of fluoroscopic images keyed toposition/orientation information as tracked by the sensors 16. Thus, themonitor 24 can render fluoroscopic images of bones in combination withcomputer generated images of virtual constructs and references togetherwith implements, instrumentation components, trial components, implantcomponents and other items used in connection with surgery fornavigation, resection of bone, assessment and other purposes.

[0080] FIGS. 2-39 are various views associated with UnicompartmentalKnee Arthroplasty surgery processes according to one particularembodiment and version of the present invention being carried out withthe FluoroNav system referred to above. FIG. 2 shows a human knee in thesurgical field, as well as the corresponding femur and tibia to whichfiducials 14 have been rigidly attached in accordance with thisembodiment of the invention. Attachment of fiducials 14 preferably isaccomplished using structure that withstands vibration of surgical sawsand other phenomenon which occur during surgery without allowing anysubstantial movement of fiducial 14 relative to body part being trackedby the system.

[0081]FIG. 3 shows fluoroscopy images being obtained of the body partswith fiducials 14 attached. The fiducial 14 on the fluoroscopy head inthis embodiment is a cylindrically shaped cage which contains LEDs or“active” emitters for tracking by the sensors 16. Fiducials 14 attachedto tibia 10 and femur 12 can also be seen. The fiducial 14 attached tothe femur 12 uses LEDs instead of reflective spheres and is thus active,fed power by the wire seen extending into the bottom of the image.

[0082] FIGS. 4-10 are fluoroscopic images shown on monitor 24 obtainedwith position and/or orientation information received by, noted andstored within computer 18. FIG. 4 is an open field with no body partimage, but which shows the optical indicia which may be used tonormalize the image obtained using a spherical fluoroscopy wave frontwith the substantially flat surface of the monitor 24. FIG. 5 shows animage of the femur 12 head. This image is taken in order to allow thesurgeon to designate the center of rotation of the femoral head forpurposes of establishing the mechanical axis and other relevantconstructs relating to of the femur according to which the prostheticcomponents will ultimately be positioned. Such center of rotation can beestablished by articulating the femur within the acetabulum or aprosthesis to capture a number of samples of position and orientationinformation and thus in turn to allow the computer to calculate theaverage center of rotation. The center of rotation can be established byusing the probe and designating a number of points on the femoral headand thus allowing the computer to calculate the geometrical center or acenter which corresponds to the geometry of points collected.Additionally, graphical representations such as controllably sizedcircles displayed on the monitor can be fitted by the surgeon to theshape of the femoral head on planar images using tactile input on screento designate the centers according to that graphic, such as arerepresented by the computer as intersection of axes of the circles.Other techniques for determining, calculating or establishing points orconstructs in space, whether or not corresponding to bone structure, canbe used in accordance with the present invention.

[0083]FIG. 5 shows a fluoroscopic image of the femoral head while FIG. 6shows an anterior/posterior view of the knee which can be used todesignate landmarks and establish axes or constructs such as themechanical axis or other rotational axes. FIG. 7 shows the distal end ofthe tibia and FIG. 8 shows a lateral view of the knee. FIG. 9 showsanother lateral view of the knee while FIG. 10 shows a lateral view ofthe distal end of the tibia.

[0084] Registration of Surgically Related Items

[0085] FIGS. 11-14 show designation or registration of items 22 whichwill be used in surgery. Registration simply means, however it isaccomplished, ensuring that the computer knows which body part, item orconstruct corresponds to which fiducial or fiducials, and how theposition and orientation of the body part, item or construct is relatedto the position and orientation of its corresponding fiducial or afiducial attached to an impactor or other other component which is inturn attached to an item. Such registration or designation can be donebefore or after registering bone or body parts as discussed with respectto FIGS. 4-10. FIG. 11 shows a technician designating with probe 26 anitem 22 such as an instrument component to which fiducial 14 isattached. The sensor 16 “sees” the position and orientation of thefiducial 14 attached to the item 22 and also the position andorientation of the fiducial 14 attached to the probe 26 whose tip istouching a landmark on the item 22. The technician designates onscreenor otherwise the identification of the item and then activates the footpedal or otherwise instructs the computer to correlate the datacorresponding to such identification, such as data needed to represent aparticular cutting block component for a particular knee implantproduct, with the particularly shaped fiducial 14 attached to thecomponent 22. The computer has then stored identification, position andorientation information relating to the fiducial for component 22correlated with the data such as configuration and shape data for theitem 22 so that upon registration, when sensor 16 tracks the item 22fiducial 14 in the infrared field, monitor 24 can show the cutting blockcomponent 22 moving and turning, and properly positioned and orientedrelative to the body part which is also being tracked. FIGS. 12-14 showsimilar registration for other instrumentation components 22.

[0086] Registration of Anatomy and Constructs

[0087] Similarly, the mechanical axis and other axes or constructs ofbody parts 10 and 12 can also be “registered” for tracking by thesystem. Again, the system has employed a fluoroscope to obtain images ofthe femoral head, knee and ankle of the sort shown in FIGS. 4-10. Thesystem correlates such images with the position and orientation of theC-arm and the patient anatomy in real time as discussed above with theuse of fiducials 14 placed on the body parts before image acquisitionand which remain in position during the surgical procedure. Using theseimages and/or the probe, the surgeon can select and register in thecomputer 18 the center of the femoral head and ankle in orthogonalviews, usually anterior/posterior and lateral, on a touch screen. Thesurgeon uses the probe to select any desired anatomical landmarks orreferences at the operative site of the knee or on the skin or surgicaldraping over the skin, as on the ankle. These points are registered inthree dimensional space by the system and are tracked relative to thefiducials on the patient anatomy which are preferably placedintraoperatively. FIG. 15 shows the surgeon using probe 26 to designateor register landmarks on the condylar portion of femur 12 using probe 26in order to feed to the computer 18 the position of one point needed todetermine, store, and display the epicondylar axis. (See FIG. 20 whichshows the epicondylar axis and the anterior-posterior plane and forlateral plane.) Although registering points using actual bone structuresuch as in FIG. 15 is one preferred way to establish the axis, a cloudof points approach by which the probe 26 is used to designate multiplepoints on the surface of the bone structure can be employed, as canmoving the body part and tracking movement to establish a center ofrotation as discussed above. Once the center of rotation for the femoralhead and the condylar component have been registered, the computer isable to calculate, store, and render, and otherwise use data for, themechanical axis of the femur 12. FIG. 17 once again shows the probe 26being used to designate points on the condylar component of the femur12.

[0088]FIG. 18 shows the onscreen images being obtained when the surgeonregisters certain points on the bone surface using the probe 26 in orderto establish the femoral mechanical axis. The tibial mechanical axis isthen established by designating points to determine the centers of theproximal and distal ends of the tibia so that the mechanical axis can becalculated, stored, and subsequently used by the computer 18. FIG. 20shows designated points for determining the epicondylar axis, both inthe anterior/posterior and lateral planes while FIG. 21 shows suchdetermination of the anterior-posterior axis as rendered onscreen. Theposterior condylar axis is also determined by designating points or asotherwise desired, as rendered on the computer generated geometricimages overlain or displayed in combination with the fluoroscopicimages, all of which are keyed to fiducials 14 being tracked by sensors16.

[0089]FIG. 23 shows an adjustable circle graphic which can be generatedand presented in combination with orthogonal fluoroscopic images of thefemoral head, and tracked by the computer 18 when the surgeon moves iton screen in order to establish the centers of the femoral head in boththe anterior-posterior and lateral planes.

[0090]FIG. 24 is an onscreen image showing the anterior-posterior axis,epicondylar axis and posterior condylar axis from points which have beendesignated as described above. These constructs are generated by thecomputer 18 and presented on monitor 24 in combination with thefluoroscopic images of the femur 12, correctly positioned and orientedrelative thereto as tracked by the system. In the fluoroscopic/computergenerated image combination shown at left bottom of FIG. 24, a“sawbones” knee as shown in certain drawings above which contains radioopaque materials is represented fluoroscopically and tracked usingsensor 16 while the computer generates and displays the mechanical axisof the femur 12 which runs generally horizontally. The epicondylar axisruns generally vertically, and the anterior/posterior axis runsgenerally diagonally. The image at bottom right shows similarinformation in a lateral view. Here, the anterior-posterior axis runsgenerally horizontally while the epicondylar axis runs generallydiagonally, and the mechanical axis generally vertically.

[0091]FIG. 24, as is the case with a number of screen presentationsgenerated and presented by the system of FIGS. 4-39, also shows atcenter a list of landmarks to be registered in order to generaterelevant axes and constructs useful in navigation, positioning andassessment during surgery. Textural cues may also be presented whichsuggest to the surgeon next steps in the process of registeringlandmarks and establishing relevant axes. Such instructions may begenerated as the computer 18 tracks, from one step to the next,registration of items 22 and bone locations as well as other measuresbeing taken by the surgeon during the surgical operation.

[0092]FIG. 25 shows mechanical, lateral, anterior-posterior axes for thetibia according to points are registered by the surgeon.

[0093]FIG. 26 is another onscreen image showing the axes for the femur12.

[0094] Any desired axes or other constructs can be created, tracked anddisplayed, in order to model and generate images and data showing anydesired static or kinematic function of the knee for any purposesrelated to a UKA.

[0095] Modifying Bone

[0096] After the mechanical axis and other rotation axes and constructsrelating to the femur and tibia are established, instrumentation can beproperly oriented to resect or modify bone in order to fit trialcomponents and implant components properly according to the embodimentof the invention shown in FIGS. 4-39. Instrumentation such as, forinstance, cutting blocks, to which fiducials 14 are mounted, can beemployed. The system can then track instrumentation as the surgeonmanipulates it for optimum positioning. In other words, the surgeon can“navigate” the instrumentation for optimum positioning using the systemand the monitor. In this manner, instrumentation may be positionedaccording to the system of this embodiment in order to align theostetomies to the mechanical and rotational axes or reference axes on anextramedullary rod that does not violate the canal, on an intramedullaryrod, or on any other type of rod. The touchscreen 24 can then alsodisplay the instrument such as the cutting block and/or the implantrelative to the instrument and the rod during this process, in order,among other things, properly to select size of implant and perhapsimplant type. As the instrument moves, the varus/valgus,flexion/extension and internal/external rotation of the relativecomponent position can be calculated and shown with respect to thereferenced axes; in the preferred embodiment, this can be done at a rateof six cycles per second or faster. The instrument position is thenfixed in the computer and physically and the bone resections are made.

[0097]FIG. 27 shows orientation of an extramedullary rod to which afiducial 14 is attached via impactor 22. The surgeon views the screen 24which has an image as shown in FIG. 29 of the rod overlain on or incombination with the femur 12 fluoroscopic image as the two are actuallypositioned and oriented relative to one another in space. The surgeonthen navigates the rod into place preferably along the mechanical axisof the femur and drives it home with appropriate mallet or other device.The present invention thus avoids the need to bore a hole in themetaphysis of the femur and place a reamer or other rod into themedullary canal which can cause fat embolism, hemorrhaging, infectionand other untoward and undesired effects.

[0098]FIG. 28 also shows the extramedullary rod being located. FIG. 29shows fluoroscopic images, both anterior-posterior and lateral, withaxes, and with a computer generated and tracked image of the rodsuperposed or in combination with the fluoroscopic images of the femurand tibia. FIG. 30 shows the rod superimposed on the femoralfluoroscopic image similar to what is shown in FIG. 29.

[0099]FIG. 29 also shows other information relevant to the surgeon suchas the name of the component being overlain on the femur image,suggestions or instructions at the lower left, and angle of the rod invarus/valgus and extension relative to the axes. Any or all of thisinformation can be used to navigate and position the rod relative to thefemur. At a point in time during or after placement of the rod, itstracking may be “handed off” from the impactor fiducial 14 to the femurfiducal 14 as discussed below.

[0100] Once the extramedullary rod, intramedullary rod, or any othertype of rod has been placed, instrumentation can be positioned astracked in position and orientation by sensor 16 and displayed on screenface 24. Thus, a cutting block of the sort used to establish thecondylar anterior cut, with its fiducial 14 attached, is introduced intothe field and positioned on the rod. Because the cutting blockcorresponds to a particular implant product and can be adjusted anddesignated on screen to correspond to a particular implant size of thatproduct, the computer 18 can generate and display a graphic of thecutting block and the femoral component overlain on the fluoroscopicimage. The surgeon can thus navigate and position the cutting block onscreen using not only images of the cutting block on the bone, but alsoimages of the corresponding femoral component which will be ultimatelyinstalled. The surgeon can thus adjust the positioning of the physicalcutting block component, and secure it to the rod in order to resect theanterior of the condylar portion of the femur in order to optimally fitand position the ultimate femoral component being shown on the screen.Other cutting blocks and other resections may be positioned and madesimilarly on the condylar component.

[0101] In a similar fashion, instrumentation may be navigated andpositioned on the proximal portion of the tibia 10 and as tracked bysensor 16 and on screen by images of the cutting block and the implantcomponent.

[0102] FIGS. 33-37 show instrumentation being positioned relative tofemur 12 as tracked by the system for resection of the condylarcomponent in order to receive a particular size of implant component.Various cutting blocks and their attached fiducials can be seen in theseviews.

[0103] Navigation, Placement and Assessment of Trials and Implants

[0104] Once resection and modification of bone has been accomplished,implant trials can then be installed and tracked by the system in amanner similar to navigating and positioning the instrumentation, asdisplayed on the screen 24. Thus, a femoral component trial, a tibialplateau trial, and a bearing plate trial may be placed as navigated onscreen using computer generated overlays corresponding to the trials.

[0105] During the trial installation process, and also during theimplant component installation process, instrument positioning processor at any other desired point in surgical or other operations accordingto the present invention, the system can transition or segue fromtracking a component according to a first fiducial to tracking thecomponent according to a second fiducial. Thus, the trial femoralcomponent is mounted on an impactor to which is attached a fiducial 14.The trial component is installed and positioned using the impactor. Thecomputer 18 “knows” the position and orientation of the trial relativeto the fiducial on the impactor (such as by prior registration of thecomponent attached to the impactor) so that it can generate and displaythe image of the femoral component trial on screen 24 overlaid on thefluoroscopic image of the condylar component. At any desired point intime, before, during or after the trial component is properly placed onthe condylar component of the femur to align with mechanical axis andaccording to proper orientation relative to other axes, the system canbe instructed by foot pedal or otherwise to begin tracking the positionof the trial component using the fiducial attached to the femur ratherthan the one attached to the impactor. According to the preferredembodiment, the sensor 16 “sees” at this point in time both thefiducials on the impactor and the femur 12 so that it already “knows”the position and orientation of the trial component relative to thefiducial on the impactor and is thus able to calculate and store forlater use the position and orientation of the trial component relativeto the femur 12 fiducial. Once this “handoff” happens, the impactor canbe removed and the trial component tracked with the femur fiducial 14 aspart of or moving in concert with the femur 12. Similar handoffprocedures may be used in any other instance as desired in accordancewith the present invention.

[0106] Alternatively, the tibial trial can be placed on the proximaltibia and then registered using the probe 26. Probe 26 is used todesignate preferably at least three features on the tibial trial ofknown coordinates, such as bone spike holes. As the probe is placed ontoeach feature, the system is prompted to save that coordinate position sothat the system can match the tibial trial's feature's coordinates tothe saved coordinates. The system then tracks the tibial trial relativeto the tibial anatomical reference frame.

[0107] Once the trial components are installed, the surgeon can assessalignment and stability of the components and the joint. During suchassessment, in trial reduction, the computer can display on monitor 24the relative motion between the trial components to allow the surgeon tomake soft tissue releases and changes in order to improve the kinematicsof the knee. The system can also apply rules and/or intelligence to makesuggestions based on the information such as what soft tissue releasesto make if the surgeon desires. The system can also display how the softtissue releases are to be made.

[0108] During this assessment, the surgeon may conduct certainassessment processes such as external/internal rotation or rotary laxitytesting, varus/valgus tests, and anterior-posterior drawer at 0 and 90degrees and mid range. Thus, in the AP drawer test, the surgeon canposition the tibia at the first location and press the foot pedal. Hethen positions the tibia at the second location and once again pressesthe foot pedal so that the computer has registered and stored twolocations in order to calculate and display the drawer and whether it isacceptable for the patient and the product involved. If not, thecomputer can apply rules in order to generate and display suggestionsfor releasing ligaments or other tissue, or using other component sizesor types. Once the proper tissue releases have been made, if necessary,and alignment and stability are acceptable as noted quantitatively onscreen about all axes, the trial components may be removed and actualcomponents navigated, installed, and assessed in performance in a mannersimilar to that in which the trial components were navigated, installed,and assessed.

[0109] At the end of the case, all alignment information can be savedfor the patient file. This is of great assistance to the surgeon due tothe fact that the outcome of implant positioning can be seen before anyresectioning has been done on the bone. The system is also capable oftracking the patella and resulting placement of cutting guides and thepatellar trial position. The system then tracks alignment of the patellawith the patellar femoral groove and will give feedback on issues, suchas, patellar tilt.

[0110] The tracking and image information provided by systems andprocesses according to the present invention facilitate telemedicaltechniques, because they provide useful images for distribution todistant geographic locations where expert surgical or medicalspecialists may collaborate during surgery. Thus, systems and processesaccording to the present invention can be used in connection withcomputing functionality 18 which is networked or otherwise incommunication with computing functionality in other locations, whetherby PSTN, information exchange infrastructures such as packet switchednetworks including the Internet, or as otherwise desire. Such remoteimaging may occur on computers, wireless devices, videoconferencingdevices or in any other mode or on any other platform which is now ormay in the future be capable of rending images or parts of them producedin accordance with the present invention. Parallel communication linkssuch as switched or unswitched telephone call connections may alsoaccompany or form part of such telemedical techniques. Distant databasessuch as online catalogs of implant suppliers or prosthetics buyers ordistributors may form part of or be networked with functionality 18 togive the surgeon in real time access to additional options for implantswhich could be procured and used during the surgical operation.

What is claimed is:
 1. A process for performing unicompartmental kneearthroplasty surgical operations on portions of a knee joint,comprising: (a) obtaining data corresponding to structure of a body partforming a portion of said joint with a locator, wherein the body partand the locator are each attached to a fiducial capable of being trackedby at least one position sensor; (b) registering a unicompartmental kneearthroplasty surgical instrument attached to a fiducial capable of beingtracked by at least one position sensor; (c) using a computer whichreceives signals from the at least one sensor, tracking position andorientation of the surgical instrument relative to the body part; (d)generating and displaying on a monitor associated with the computer avisual image of the instrument properly positioned and oriented relativeto the body part; (e) navigating the instrument relative to the bodypart and attaching the instrument to the body part according to theimage; and (f) modifying the body part using the instrument attached tothe body part; and (g) assessing performance of the joint using imagesdisplayed on said monitor.
 2. The process of claim 1, further comprisingregistering a body part by intraoperatively designating at least onepoint on the body part with a probe, wherein the probe is attached to afiducial capable of being tracked by said at least one position sensor.3. The process of claim 1, wherein the body part comprises one of afemur, a tibia and a patella.
 4. The process of claim 1, wherein thelocator comprises one of a C-arm fluoroscope, a CT scanner, MRIequipment, ultrasound equipment, laser scanning equipment and a probe.5. The process of claim 1, wherein the fiducials comprise one of activefiducials, passive fiducials and hybrid active/passive fiducials.
 6. Theprocess of claim 1, wherein the position tracking sensors comprise oneof infrared sensors, electromagnetic sensors, electrostatic sensors,light sensors, sound sensors, and radiofrequency sensors.
 7. The processof claim 1, wherein the surgical instrument comprises a rod and acutting block.
 8. A process for performing unicompartmental kneearthroplasty surgical operations on portions of a knee joint comprising:(a) obtaining data corresponding to structure of a body part forming aportion of said joint with a locator, wherein the body part and thelocator are each attached to a fiducial capable of being tracked by atleast one position sensor; (b) registering a unicompartmental kneearthroplasty surgical instrument attached to a fiducial capable of beingtracked by at least one position sensor; (c) using a computer whichreceives signals from the at least one sensor, tracking position andorientation of the instrument relative to the body part; (d) generatingand displaying on a monitor associated with the computer a visual imageof the instrument properly positioned and oriented relative to the bodypart; (e) navigating the instrument relative to the body part andattaching the instrument to the body part according to the image; (f)modifying the body part using the instrument attached to the body part;(g) removing the instrument from the body part; (h) registering aunicompartmental knee arthroplasty trial component attached to afiducial capable of being tracked by at least one position sensor; (i)tracking position and orientation of the trial component relative to thebody part; (j) generating and displaying on the monitor a visual imageof the trial component properly positioned and oriented relative to thebody part; (k) navigating and installing the trial component on the bodypart according to the image; and (l) assessing performance of the kneejoint using images displayed on the monitor.
 9. The process of claim 8,further comprising: (a) discontinuing tracking of the trial componentusing the fiducial attached to the trial component; and (b) initiatingtracking of the trial component using the fiducial attached to the bodypart on which the trial component is installed.
 10. The process of claim8, wherein the body part comprises one of a femur, a tibia and apatella.
 11. The process of claim 8, wherein the locator comprises oneof a C-arm fluoroscope, a CT scanner, MRI equipment, ultrasoundequipment, laser scanning equipment and a probe.
 12. The process ofclaim 8, wherein the fiducials comprise one of active fiducials, passivefiducials and hybrid active/passive fiducials.
 13. The process of claim8, wherein the position/orientation tracking sensors comprise at leastone of infrared sensors, electromagnetic sensors, electrostatic sensors,light sensors, sound sensors, and radiofrequency sensors.
 14. Theprocess of claim 8, wherein the trial component comprises a femoralcomponent.
 15. The process of claim 8, further comprising: (a)performing soft tissue balancing tests while the computer continues totrack the fiducials; (b) using data generated by the computer, includinginformation related to at least one of release points and amounts, toassess alignment and stability of the trial component and the kneejoint; and (c) releasing soft tissue to adjust alignment and stabilityof the knee joint.
 16. A process for performing unicompartmental kneearthroplasty surgical operations on portions of a knee joint comprising:(a) obtaining data corresponding to the structure of a body part forminga portion of said joint with a locator, wherein the body part and thelocator are each attached to a fiducial capable of being tracked by atleast one position sensor; (b) registering a unicompartmental kneearthroplasty trial component attached at least indirectly to a fiducialcapable of being tracked by at least one position sensor; (c) using acomputer which receives signals from the at least one sensor, trackingposition and orientation of the trial component relative to the bodypart; and (d) generating and displaying on a monitor associated with thecomputer a visual image of the trial component properly positioned andoriented relative to the body part.
 17. A process for performingunicompartmental knee arthroplasty surgical operations on portions of aknee joint comprising: (a) obtaining data corresponding to structure ofa body part forming a portion of said joint with a locator, wherein thebody part and the locator are each attached to a fiducial capable ofbeing tracked by at least one position sensor; (b) registering aunicompartmental knee arthroplasty implant trial component attached atleast indirectly to a fiducial capable of being tracked by at least oneposition sensor; (c) using a computer which receives signals from the atleast one sensor, tracking position and orientation of the trialcomponent relative to the body part; (d) generating and displaying on amonitor associated with the computer a visual image of the trialcomponent properly positioned and oriented relative to the body part;(e) navigating the trial component relative to the body part andattaching the trial component to the body part according to the image;(f) performing soft tissue balancing tests while the computer continuesto track the fiducials; (g) using data generated by the computer toassess alignment and stability of the joint with the trial componentattached; and (h) releasing soft tissue to adjust alignment andstability.
 18. A process for performing unicompartmental kneearthroplasty surgical operations on portions of a knee joint comprising:(a) obtaining data corresponding to structure of a body part forming aportion of said joint with a locator, wherein the body part and thelocator are each attached to a fiducial capable of being tracked by atleast one position sensor; (b) registering a unicompmaratmental kneearthroplasty implant component attached at least indirectly to afiducial capable of being tracked by at least one position sensor; (c)using a computer which receives signals from the at least one positionsensor, tracking position and orientation of the implant componentrelative to the body part; (d) generating and displaying on a monitorassociated with the computer a visual image of the implant componentproperly positioned and oriented relative to the knee joint; and (e)navigating the implant component relative to the body part and attachingthe implant component to the body part according to the image.
 19. Theprocess of claim 18, further comprising performing soft tissue balancingtests on the joint with implant component installed while the computercontinues to track the fiducials.
 20. A process for performingunicompartmental knee arthroplasty surgical operations on portion of aknee joint comprising: (a) obtaining data corresponding to structure ofa body part forming a portion of said joint with a locator, wherein thebody part and the locator are each attached to a fiducial capable ofbeing tracked by at least one position sensor; (b) registering aunicompartmental knee arthroplasty implant component attached to a toolto which is attached a fiducial capable of being tracked by at least oneposition sensor; (c) using a computer which receives signals from the atleast one sensor, tracking position and orientation of the implantcomponent relative to the body part; (d) generating and displaying on amonitor associated with the computer a visual image of the implantcomponent properly positioned and oriented relative to the body part;(e) navigating the implant component relative to the body part andattaching the implant component to the body part according to the image;(f) discontinuing tracking of the implant component using the fiducialattached to the tool; (g) initiating tracking of the implant componentusing the fiducial attached to the body part on which the implantcomponent is attached; (h) performing soft tissue balancing tests whilethe computer continues to track the fiducials; and (i) using datagenerated by the computer to assess alignment and stability of the jointwith the implant installed.
 21. A system for performing unicompartmentalknee arthroplasty surgical operations on portions of a knee jointcomprising: (a) an imager for obtaining an image of a femur, wherein theimager and the femur are each attached to a fiducial capable of beingtracked by a position sensor; (b) at least one position sensor adaptedto track position of said fiducials; (c) a computer adapted to store atleast one image of the femur and to receive information from said atleast one sensor in order to track position and orientation of saidfiducials and thus the femur; (d) an extramedullary rod adapted to beattached to a femur using an impactor, said impactor attached to afiducial, whereby the position of the extramedullary rod is capable ofbeing tracked by said sensor and the position and orientation of the rodis capable of being tracked by said computer; and (e) a monitor adaptedto receive information from the computer in order to display at leastone image of said extramedullary rod positioned and oriented relative tothe femur for navigation and positioning of the rod on the femur.
 22. Asystem for performing unicompartmental knee arthroplasty surgicaloperations on portions of a knee joint comprising: (a) an imager forobtaining an image of a femur, wherein the imager and the femur are eachattached to a fiducial capable of being tracked by a position sensor;(b) at least one position sensor adapted to track position of saidfiducials; (c) a computer adapted to store at least one image of thefemur and to receive information from said at least one sensor in orderto track position and orientation of said fiducials and thus the femur;(d) a medullary rod adapted to be attached to a femur using an impactor,said impactor attached to a fiducial, whereby the position of themedullary rod is capable of being tracked by said sensor and theposition and orientation of the rod is capable of being tracked by saidcomputer; and (e) a monitor adapted to receive information from thecomputer in order to display at least one image of said medullary rodpositioned and oriented relative to the femur for navigation andpositioning of the rod on the femur.
 23. A system for performingunicompartmental knee arthroplasty surgical operations on portions of aknee joint comprising: (a) a locator for obtaining data corresponding tothe structure of bone, wherein the locator and the bone are eachattached to a fiducial capable of being tracked by a position sensor;(b) at least one position sensor adapted to track position of saidfiducials; (c) a computer adapted to store data relating to structure ofthe bone and to receive information from said at least one sensor inorder to track position and orientation of said fiducials and thus thebone; (d) a unicompartmental knee arthroplasty surgical instrumentadapted to be associated with a fiducial which is attached to bone,whereby the position and orientation of the instrument is capable ofbeing tracked by said sensor; and (e) a monitor adapted to receiveinformation from the computer in order to display at least one image ofthe instrument and a unicompartmental knee arthroplasty implantcomponent corresponding to said instrument, positioned and orientedrelative to the knee joint for navigation and positioning of theinstrument on the bone.
 24. A system for performing unicompartmentalknee arthroplasty surgical operations on portions of a knee jointcomprising: (a) an imager for obtaining an image of a femur, wherein theimager and the femur are each attached to a fiducial capable of beingtracked by a position sensor; (b) at least one position sensor adaptedto track position of said fiducials; (c) a computer adapted to store atleast one image of the femur and to receive information from said atleast one sensor in order to track position and orientation of saidfiducials and thus the femur; (d) a femoral trial implant capable ofbeing mounted on a tool, said tool attached to a fiducial, whereby theposition of the femoral trial implant is capable of being tracked bysaid sensor and the position and orientation of the trial implant iscapable of being tracked by said computer; and (e) a monitor adapted toreceive information from the computer in order to display at least oneimage of said femoral trial implant positioned and oriented relative tothe femur for navigation and positioning of the trial implant on thefemur.
 25. A system for performing unicompartmental knee arthroplastysurgical operations on portions of a knee joint comprising: (a) animager for obtaining an image of a tibia, wherein the imager and thetibia are each attached to a fiducial capable of being tracked by aposition sensor; (b) at least one position sensor adapted to trackposition of said fiducials; (c) a computer adapted to store at least oneimage of the tibia and to receive information from said at least onesensor in order to track position and orientation of said fiducials andthus the tibia; (d) a tibial trial implant capable of being mounted on atool, said tool attached to a fiducial, whereby the position of thetibial trial implant is capable of being tracked by said sensor and theposition and orientation of the trial implant is capable of beingtracked by said computer; and (e) a monitor adapted to receiveinformation from the computer in order to display at least one image ofsaid tibial trial implant positioned and oriented relative to the bodypart for navigation and positioning of the trial implant on the tibia.26. A system for performing unicompartmental knee arthroplasty surgicaloperations on portions of a knee joint comprising: (a) an imager forobtaining an image of a femur, wherein the imager and the femur are eachattached to a fiducial capable of being tracked by a position sensor;(b) at least one position sensor adapted to track position of saidfiducials; (c) a computer adapted to store at least one image of thefemur and to receive information from said at least one sensor in orderto track position and orientation of said fiducials and thus the femur;(d) a femoral implant capable of being mounted on a tool, said toolattached to a fiducial, whereby the position of the femoral implant iscapable of being tracked by said sensor and the position and orientationof the implant is capable of being tracked by said computer; and (e) amonitor adapted to receive information from the computer in order todisplay at least one image of said femoral implant positioned andoriented relative to the femur for navigation and positioning of theimplant on the femur.
 27. A system for performing unicompartmental kneearthroplasty surgical operations on portions of a knee joint comprising:(a) an imager for obtaining an image of a tibia, wherein the imager andthe tibia are each attached to a fiducial capable of being tracked by aposition sensor; (b) at least one position sensor adapted to trackposition of said fiducials; (c) a computer adapted to store at least oneimage of the tibia and to receive information from said at least onesensor in order to track position and orientation of said fiducials andthus the tibia; (d) a tibial implant capable of being mounted on animpactor, said impactor attached to a fiducial, whereby the position ofthe tibial implant is capable of being tracked by said sensor and theposition and orientation of the implant is capable of being tracked bysaid computer; and (e) a monitor adapted to receive information from thecomputer in order to display at least one image of said tibial implantpositioned and oriented relative to the femur for navigation andpositioning of the implant on the tibia.
 28. A system for performingunicompartmental knee arthroplasty surgical operations on portions of aknee joint comprising: (a) a locator for obtaining data corresponding tostructure of a femur, wherein the locator and the femur are eachattached to a fiducial capable of being tracked by a position sensor;(b) at least one position sensor adapted to track position of saidfiducials; (c) a computer adapted to store at least one image of thefemur and to receive information from said at least one sensor in orderto track position and orientation of said fiducials and thus the femur;(d) a unicompartmental knee arthroplasty surgical instrument whoseposition is capable of being tracked by said sensor and whose positionand orientation is capable of being tracked by said computer; (e) afemoral trial implant capable of being mounted on a tool, said toolattached to a fiducial, whereby the position of the femoral trialimplant is capable of being tracked by said sensor and the position andorientation of the trial implant is capable of being tracked by saidcomputer; (f) a femoral implant capable of being mounted on a tool, saidtool attached to a fiducial, whereby the position of the femoral implantis capable of being tracked by said sensor and the position andorientation of the implant is capable of being tracked by said computer;and (g) a monitor adapted to receive information from the computer inorder to display at least one image of said instrument, at least oneimage of said femoral trial implant and at least one image of saidfemoral implant positioned and oriented relative to the femur fornavigation and positioning of the instrument, the trial implant, and theimplant on the femur.
 29. A system for performing unicompartmental kneearthroplasty surgical operations on portions of a knee joint comprising:(a) a locator for obtaining data corresponding to structure of a tibia,wherein the locator and the tibia are each attached to a fiducialcapable of being tracked by a position sensor; (b) at least one positionsensor adapted to track position of said fiducials; (c) a computeradapted to store at least one image of the tibia and to receiveinformation from said at least one sensor in order to track position andorientation of said fiducials and thus the tibia; (d) aunicomparatmental knee arthroplasty surgical instrument whose positionis capable of being tracked by said sensor and whose position andorientation is capable of being tracked by said computer; (e) a tibialtrial implant capable of being mounted on a tool, said tool attached toa fiducial, whereby the position of the tibial trial implant is capableof being tracked by said sensor and the position and orientation of thetrial implant is capable of being tracked by said computer; (f) a tibialimplant capable of being mounted on a tool, said tool attached to afiducial, whereby the position of the tibial implant is capable of beingtracked by said sensor and the position and orientation of the implantis capable of being tracked by said computer; and (g) a monitor adaptedto receive information from the computer in order to display at leastone image of said instrument, at least one image of said tibial trialimplant and at least one image of said tibial implant positioned andoriented relative to the femur for navigation and positioning of theinstrument, the trial implant and the implant on the tibia.